Photographic type face reproducers

ABSTRACT

The signals required to control reproduction of characters on the print-out cathode ray tube in a photo-typesetting machine consist of a series of binary codes indicating successive line positions in a raster at which the beam is to be switched on and off in re-forming a character on the print-out tube. To create such a binary code series, a ring of transparent characters on a rotary opaque carrier (or vice-versa) are selectively illuminated from one side of the ring for flooding each required character in turn as the carrier rotates and a line of miniature photo-diode devices is arranged on the other side of the ring in scanning position relative to the illuminating means to detect and signal the physical two-dimensional position on a raster basis in a character area of each ON and OFF change in illumination on the diodes. Detector means successively scan the photo-diodes at high speed relative to the rotational speed of the character carrier and detect the ON and OFF changes in their electrical condition the coordinate positions of which in a character area are signalled to code-responsive means.

United States Patent [1 91 Kyte a [111 3,814,848 '[451 June 4, 1 974 [5 1 PHOTOGRAPHIC TYPE FACE REPRODUCERS [76] Inventor: Derek John Kyte, 117, Valley Rd.,

Chorley Wood, England 22 Filed: Nov. 30, 1972 21 Appl. No.: 310,683

[30] Foreign Application Priority Data Dec. 9, 1971 Great Britain 57421/71 [52] US. Cl 178/7.l, l78/D1G. 27, 340/224 R, 340/173 LM, 340/346 DD [51] Int. Cl. H04n 1/06 [58] Field of Search 178/76, 7.1, 6.8, l5, 178/30, DlG. 27; 340/324 R, 324 AD, 173 LM, 346 DD [56] References Cited UNITED STATES PATENTS 2,905,897 9/1959 Giel 340/173 LM 3,056,955 10/1962 Dirks 340/347 DD 3,201,780 8/1965 Gryk 340/347 DD 3,229,047 1/1966 Simpson 340/173 LM 3,692,935 9/1972 Manber 178/15 Primary E.raminer-H0ward W. Britton Attorney, Agent, or Firm-Darbo, Robertson & Vandenburgh [57] ABSTRACT The signals required to control reproduction of characters on the print-out cathode ray tube in a phototypesetting machine consist of a series of binary codes indicating successive line positions in a raster at which the beam is to be switched on and off in re-forming a character on the print-out tube.

To create such a binary code series, a ring of transparent characters on a rotary opaque carrier (or vice-versa) are selectively illuminated from one side of the ring for flooding each required character in turn as the carrier rotates and a line of miniature photo-diode devices is arranged on the other side of the ring in scanning position relative to the illuminating means to detect and signal the physical two-dimensional position on a raster basis in a character area of each ON and OFF change in illumination on the diodes.

Detector means successively scan the photo-diodes at high speed relative to the rotational speed of the character carrier and detect the ON and OFF changes in their electrical condition the coordinate positions of which in a character area are signalled to code-responsive means.

7 Claims, 4 Drawing Figures PATENTEnJun 4 1974 'SHEET 2 OF 3 TLC VFF

PDC

AGS

DPD

CCT

CRS

FIG 3 PATENTEDJUN 419M 1814-848 sum 3 or 3 SECTION THROUGH ROTA'TING DRUM Cl L5! 3 L2 L52 LP LS4 L4 BACKGROUND OF THE INVENTION In the photo-typesetting art it is wellknown to produce characterimageson the face of a print-out cathode ray tube by the fast movingelectron beam and photograph the results direct on to photo-sensitive film or In such systems, for each character'image produced on the cathode ray tube (hereinafter C.R.T.),.the electron beam produces a scanning-character images in matrix form on a photographic master. lines. During the scanning of each line, the beam current is switched OFF and ON so that only those parts of the line outside the confines of the character image give visible light from the phosphor screen.

The signals required to control the character reproduction on the print-out C.R.T. can be produced by utilising a flying spot scanner C.R.T. SCANNING CHAR- ACTER IMAGES IN MATRIX FORM ON'A PHOTO-v GRAPHIC MASTER. In a directly-operating system of this' kind, the scanner is operated in synchronism with the print-out C.R.T. so that the brightness of the light spot of the latter is controlled by the video signal obter basis in a character area of each ON and OFF change in the secondary illumination.

To create such a binary code series, a ring of transparent characters on .a rotary opaque carrier (or'vice versa) are selectively illuminated from one side of the ring for flood lighting each required character in turn as the carrier rotates, and a line of miniature photodiode devices arranged on the other side of the ring and in scanning position relative to the illuminating means.

Detector means successively scan the photodiode devices at high speed relative to the rotational speed of tained from the simultaneous scanning of a selected character on the master matrix.

Such a method has the advantage that the basic storage of the required information is in photographic form and is reasonably cheap. Access to this information is however expensive and complex.

In another known source of character signals each character shape is coded into a series of binary codes indicating successive line positions at which the beam is switched ON or OFF. These codes are. permanently stored in a computer store, so that the group of codes for any desired character can be extracted for use in reforming the character on a print-out tube.

However very large amounts of storage are'required when as is usual many different type faces in many different sizes are required.

It is also known to utilise temporary storage between flying spot scanners and print-out C.R.Ts..

SUMMARY OF THE INVENTION This invention relates to type-face reproducers suiting binary-coded information representative of the.

shape of characters, and consists essentially of equipment-for generating coded electrical information defining the shape of visual characters comprising means for illuminating through the air a character on a photo- 1 differential background and thereby creating secondary airborne illumination embodying the character shape, and photo-responsive means physically arranged for illumination in air by said secondary airborne illumination and electrically arranged for detecting and sig nalling the physical two-dimensional position on a rasthe character carrier and detect the ON and OFF changes in their electrical condition, the coordinate positions of which in a character area are signalled to code responsive means.

DESIGNATION OF THE FIGURES characters on the rotary matrix; and

FIG. 4 is a schematic representation of the scanning arrangements for a coordinate array of characters on the-rotary matrix.

DESCRIPTION OF PREFERRED EMBODIMENTS One or more sets of characters in negative form on a photographic film strip S are held on the circumfcrence of a transparent (or partly transparent) cylinder C which is caused to rotate at constant speed by a motor MO.

A light source (e.g., a tungsten lamp) LS illuminates a diaphragm D'via a lens L1. The diaphragm D has a circular or rectangular hole whichis focussed by means of a lens L2 and a plane mirror M on to the surface of the film strip 5. The optical constants and the size of the hole in the diaphragm are arranged such that the patch of light on the film strip is at least as large as the largest character.

Alternately, a simple light source flooding a rectangular section light beam generator can be provided adjacent the film strip.

Light emerging from the illuminated character is focussed by lens L3 so that an image of the character is formed in the plane P. I

In this plane P is placed-a linear photo-diodearray .PDA such that the direction of the array is parallel to the axis of the rotating cylinder and is thus vertical with respect to the characters on the film strip.

The photo-diode array is shown diagrammatically in FIG. 2. It consists of a series of small photo-diodes placed close together in a straight line. Such arrays are manufactured out of one or two semiconductor slices and are available from several manufacturers of integrated circuits.

The arrays have typically 256 separate diodes and have a built-in sequential sampler (or dynamic shift counter) SS, FIG. 3, which permits the signal from each of the photo-diodesto be sampled sequentially on application of suitable control signals.

An example of such a device is the State Line Scanner made by the Reticon Corporation, 365 Middle'field Road, Mountain View, California, USA, and marketed in Europe, for instance by Walmore Electronics Limited, 11 l5, Betterton Street, Drury Lane, Lon don, WCZH 988, in which the drive circuit for the shift counter is fed from a simple pulse train such as that from the oscillator OS, FIG. 3.

Although not essential for the operation of the invention, two further features are shown on FIG. 1 which make the system easier to produce and operate.-

Before each character on the film strip is a thin transparent line which marks the beginning of the area occupied by that character.'This line (known in typography as the side bearing) does not normally touch the character but is separated from it by a short distance because, of course, printed characters in practice are separated by a small amount of white space. v

The lower part of the line protrudes beneath the lowest point of any character. This part is also illuminated, either by the main light souce LS or by a subsidiary system. An image is formed external to the drum by a lens (not shown). In the same vertical line as the linear photodiode array, but lower down, is placed a single photodiode SC. The purpose of this diode is to detect the start of a character by giving a pulse as the image of-the thin start character line passes across it.

At some point on the film strip, normally at the beginning of the character'set, are two thin vertical lines placed very close together as illustrated at DS in FIG. 1. v

The start character diode SC senses these two lines and gives a double pulse which is used by the control circuits explained later.

Also, at the lower edge of the rotating drum is shown a film strip' containing a series of closely spaced parallel lines G. These lines are also illuminated by a light source (not shown) and are sensed by the photodiode DF. This diode, therefore, emits a series of electrical pulses the frequency of which is proportional to the speed of the drum. If desired, the lines G may cooperate with a set of micrometer lines on a superposed static film strip to form by the well-known Moire Fringe technique, a pulse train of a higher order of frequency on diode DF. The prime purpose of this system is to ensure that the control circuits operate in synchronism with the drum speed. They are not essential when the drum speed is closely controlled by other means.

The control circuitry is shown in block diagram form in FIG. 3.

The blockCCT is the character counter and consists of a simple binary counter with a capacity at least equal to the number of characters around the drum. If this is 127, the counter CCT will have 7 stages. I

The block marked DPD is a double pulse detector.

Both this and the counter CCT' are connected to the photo-diode SC, FIG. I.

It will be remembered that the photo-diode SC gives two pulses close together when the image of the double line DS passes across it. The circuit DPD detects this occurrance and resets the counter CCT to zero. Thereafter, each time that the diode SC sees one of the start character lines, the counter CCT is advanced by one. Thus this counter keeps track of which character is passing through the illuminated area of the drum surface.

The outputs from each binary stage of the counter CCT (typically eight in all) are fed to a coincidence detector CD. Also feeding CD are the equivalent binary stage outputs from a code request store CRS which has been supplied with a binary code CR representing the character required to be scanned and digitised. This code may well be supplied by a computer controlling the whole system.

When the code requested is equal to the code in the character counter CCT, the coincidence counter will give an output pulse on line SSP.

This pulse performs three functions. First, it resets via RES], the linear photo-diode array shift counter SS which controls the sequential activities of the vertical photo-diode array PDA in the plane P, FIG. 1.

Secondly, pulse SSP resets via RES2, a binary counter PDC whose purpose is explained below.

Finally, pulse SSP sets the scan flip-flop SF Fl which starts the whole process of scanning and digitising of the particular character selected.

While the drum is rotating, it will be remembered that the photodiode DF is giving out a continuous stream of pulses proportional to the speed of rotation of the drum. These pulses appear on line DF in FIG. 3 and are fed to a frequency divider FD. The output of this circuit is also a continuous stream of pulses synchronised to, but not necessarily at the same frequency as those from the photo-diode DF.

These pulses are differentiated to produce a series of narrow spikes.

When the AND gate AG] is primed by the setting of the scan flip-flop SFFl, the next spike from divider FD will pass through AG] and set the second start flip-flop SFFZ. This flip-flop now primes AND gate AGZ so that high-frequency pulses from an oscillator OS are allowed to control the shift counter SS connected to the photo-diode array PDA. The frequency of the oscillator OS must be at least as high as theproduct of the frequency of the spikes from divider FD and the number of photodiodes in the array PDA so that the array is completely scanned once between each adjacent pair of spikes, In practice, the frequency should be somewhat higher than this product to give a reasonable safety margin to this system. For modern photo-diode devices, this frequency can be of the order of IO Mc/s. Each pulse that enters the counter SS causes the system to sample the next photo-diode in the array. The corresponding photo-diode signal appears on the output line VO from SS. At the same time that the pulses cause counter SS to sample successive diode signals, they also increment a binary counter PDC. Thus counter PDC contains the number of the diode in the array which is being sampled at any time.

As the image of the selected character passes across the photo-diode array, at any instant in time some of the diodes will be illuminated and some not. During the scan of the state of each diode the output signal V0 is passed throughthreshold and limiting circuits TLC so that it is either an on or off signal. It then passes to the input of a flip-flop VFF which changes its state whenever the V0 signal makes a transition from high to low or vice versa, that is, when the sampling shift register passes from an illuminated diode to a dark diode or vice versa.

Each time flip-flop VFF changes its state, a short pulse will be generated by either of the two one-shot circuits O81, 052. This pulse, after passing through the OR gate 0R1 primes a set of AND gates AGS which image the components of the pDC counter so that the state of the counter (i.e., the number of the photodiode at which the transition occurs) is passed as a binary code to a Digital Memory DM.

This sequence continues, the number of each diode where a change of illumination level occurs being passed in binary coded form into the memory block DM.

Eventually, the counter PDC will be full, this state corresponding to the end of a complete scan along the diode array PDA. This state is recognised by the AND gate AG3, which now gives an output since all inputs are at logical l, for instance. The output generates a pulse via one-shot circuit OS3 and the full state of the counter PDC is passed by AGS to the memory DM as an all ls code.

This code can also be used to signal to a lines per character counter LPC described below successive line scans through a character.

On the next pulse into the shift counter SS the output from theAND gate AC3 drops to zero and signals via one-shot circuit 054 to reset the flip-flop SFF2 so that no more pulses are fed to the photo-diode shift counter SS until the next spike from divider FD is received. Thus the scans of the diodearray are synchronised with the pulses from F3 and hence to the speed of the drum. This ensures that the scans are made ata prescribed number per inch of drum movement (typically 650 per inch) irrespective of the actual drum speed.

Becuase characters for quality typographic reproduction vary in'width, the number of linear scans which must be made varies from character to character. For example, over three times as many scans are necessary to cover an M as for an i.

The number of linear scans to completea character must, therefore, be controlled according to the character being scanned. This information is usually available in a photo-setting system in a binary coded form, especially if the system is computer-controlled.

The assumption here, therefore, is that when the character code is fed to the code request store CRS, the number of lines NL required to describe that character is simultaneously fed to a Lines per Character counter LPC, of the count-downv type. As stated above, end of line pulses from AC3 are fed to LPC during the scanning of a character until the number of pulses fed in equals the number NL put into it, when the all zero) condition operates gate A04.

Recapitulating, it will be seen that at the end of each scan through the diode array, the LPC counter is fed,

with a pulse from the AND gate AC3 as the input to this gate drops to zero. When the required number of scans have been made the AND gate A03 and the outputs to gate AC4 are all zero, gate AC4 will give out a pulse which resets the start flipflop SFFl. The scanning of the whole character is now complete and the process stops until another character is requested by sending a new code to the code request store CR8 and a new number to LPC.

Summarising the action of the whole system, a computer or other device calls for a character by sending a binary code to the "code request store CR5 and, at the same time, sending a number representing the width of the character to the Lines per Character counter (LPC). When the required character appears in the field of illumination, the linear photodiode array I is scanned sequentially in synchronism with the motion of the drum for a given number of times.

Binary codes corresponding to the character shape are fed sequentially into the Digital Memory DM the end of each photo-diode scan being marked with a special code (all ones'). It will be seen that the stored information is idential in form with that stored in the permanent computer store technique described in the opening paragraphs.

lt is evident that this binary information can be used ,to recreate the image of a character on the face of a cathode ray tube in the well-known conventional manner. The beam is made to describe a series of vertical sweeps in raster form. A binary counter starts to count up from zero at the beginning of each sweep. When the number in the counter coincides with the first stored binary code for that line, the CRT beam is switched on. It remains on until coincidence occurs with the next number and so on.

The nature of the Digital Memory DM depends on the use to which the system is being put.

In the simplest system, where each character is called for in turn and the print-out system waits until it has been scanned and digitised, the store DM could conveniently take the form of a static shift register capable of storing the maximum number of codes needed to describe a whole character. For characters up to 36 pts. in size, (i.e., about one-half inch), a static shift register to hold 1,024 codes would be satisfactory. Such devices are available cheaply on integrated circuit chips.

A system of the above type would, however, be comparatively slow because it would be necessary to wait, on an average, for half a drum revolution for every character. At a typical drum speed of about 13 revolutions per second, this would give an output speed of about 26 characters/second.

However, by making the digital memory DM of greater capacity, the speed of the system can be increased. ln this case, the store would conveniently take the form of a short shift register (holding only a few codes) followed by a random access memory in known manner. The latter could well form part of the core store of a computer.

In this type of system, the computer would analyse the next, say, five characters to be printed, arrange them in the order that they appear on the drum as already known, and'send code requests in that order to the digitiser. Thus in not more than one drum revolution, five digitised characters would be in the memory. As these characters are printed out, (not in the order in which they have been scanned but in the order in which they were originally received) the next five characters are called for and so on. In this way, the average output speed can be increased to be better than characters per second. Speed can also be increased by using more than one linear diode array, in conjunction with additional means for illuminating other positions on the drum. For example, two such arrays arranged at opposite points of the rotating drum would double the access speed without increasing the size of the temporary digital memory.

Furthermore, it will be apparent that the scanning device can have more than one character set. Several such sets could be arranged one above the other and accessed in known manner either by (a) moving the rotating drum vertically into different positions, or (b) by moving the source of illumination and the linear diode array. Alternatively, several lenslets one for each character set could be used as shown diagrammatically in FlG. 4. The lenslets L, to L focus the corresponding illuminated characters C l to C4 ontoa single area in which is placed a single linear diode array LP. To select one of the four character sets, only one of the 4 light sources LS1 to LS4 is switched on. Alternatively, all light sources are allowed to remain on and the light beams not required could be shuttered off with electro-magnetically operated shutters.

in describing the system this far, the size of the characters has not been considered. In practice, characters will need to be reproduced over a wide range of sizes.

When considering the vertical height of characters, it will be clear that on the output cathode ray tube system, any size of vertical scan line could be reproduced by merely'altering the vertical deflection amplitude. However, the vertical definition of the system is fixed by the number of diodes in the linear array and it is not, therefore, possible to enlarge the final image indefinitely without loss in image quality. if we assume that there are 256 diodes in the array and that the desirable character definition is 650 lines/inch, then characters up to about 4 inches high (about 30 pts) could be reproduced satisfactorily.

in the horizontal direction, the number of scan lines needed to describe a character will increase with character size. Thus an M in 30 pts. will need twice as many scan lines as an M at 15 pts., if the final definition of the printed character is to be constant.

in the scan system described, it is possible to operate at a constant horizontal definition at the scanning stage and to use variable definition at the print-out stage. Thus if 100 scan lines are used to scan an M, the same number of lines will be used to describe the M at the print out stage irrespective of its size. This method is acceptable over a limited range of sizes. In general, however, it is preferable to work at constant definition on the print-out. This requires that the number-of scan lines per character at the scanning stage be changed accordingto final size.

in practice, this can be achieved in the scanning system described by altering the rate at which the linear photo-diode array is scanned relative to the drum speed. This is the purpose of the frequency divider block FD in FIG. 3. By dividing the pulse frequency from the diode DF by different constants, the scans per inch of-drum movement can be varied. Thus if the divi-' sion factor was one for characters to be reproduced at 30 pts., it would be two for characters at 15 pts., etc.

At some stage, the speed of rotation of the drum and i the number of scan lines per character will be such that the limiting frequency of the linear photo-diode system will be reached. At this point, it is not possible to increase the scanning resolution without decreasing the drum speed. Since this would affect access time, the preferred method of operation would be to optimise drum speed to give minimum access time and satisfactory definition for characters in the range of sizes from 5 l2 pts. and then to slow the drum to half-speed for characters in the range 12 24 pts.

Although the. linear photo-diode array is a convenient and cheap way of implementing the system described, it is also possible to achieve similar results by 65 a series of coincident lines, and an image of the scan line position on the screen focussed onto the rotating drum. The emergent light from the scanning of a char acter on the drum would be picked up by a lens system and passed to a photomultiplier tube, the output of which would be passed to line VO, FIG. 4.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a device for producing a plurality of electrical signals for typesetting purposes which signals define the shape of a number of visual characters such as letters of the alphabet or the like, the improvement comprismg:

a character carrier member, a scanning member, means connected to one of said members to move it repeatedly along a given path with respect to the other member so that there is cyclical relative motion between the members along said path with the motion being at a given rate, said character carrier member having means to visually display each of said characters against a photo-differential background in a sequential series parallel to said path so that with said relative motion there is first an approach to a character, then a stage of movement adjacent that character and then a separation from the next character in turn and the scanning member, with said stage of movement adjacent the character taking place in a given period of time, said carrier member having indexing means indicative of which character is in said stage, said scanning member including means for scanning transversely of said path at a rate such that a plurality of sweeps across each character takes place during said stage whereby during each sweep an electrical signal is produced which signal represents a portion of the character and at the time of the subsequent sweep there has been relative motion between the character and the scanning member so that said subsequent sweep traverses, and produces electrical signals indicative of, an adjacent portion of the character, said scanning member including means positioned to sense and respond to said indexing for identifying which character is in said stage.

2. In a device as set forth in claim 1, wherein said carrier member comprises a rotatable drum having an inside and an outside and having portions which are at least partially transparent and portions which are non-transparent, which portions define said characters and also define lines at each side of each character which lines form part of said means for identifying which character is in said stage, and means at one of said sides of the drum for shining light through the at least partially transparent portions to produce said visual display, and

said scanning member is stationary on the other of said sides of the drum in a position at which the light from said at least partially transparent portions falls on said scanning means.

3. In a device as set forth in claim 1, wherein said means for scanning transversely comprises a plurality of photodiodes positioned sequentially in a line generally normal to said path with the end diodes in the sequence being spaced apart sufficient to extend across the corresponding dimension of said visual display.

4. in a device as set forth in claim 3, wherein said carrier member comprises a rotatable drum having an inside and an outside and having portions which are at least partially transparent and portions which are non-transparent, which portions define said characters and also define lines at each side of each character which lines form part of said means for identifying which character is in said stage, and means at one of said sides of the drum for shining light through the at least partially transparent portions to produce said visual display, and

said scanning member is stationary on the other of said sides of the drum in a position at which the light from said at least partially transparent portions falls on said scanning means.

5. ln 2! device as set forth in claim 1, wherein said indexing means includes a visual mark transverse to said path and positioned between each character and further visual marking means to identify each time that the cycle of relative movement repeats.

6. ln a device as set forth in claim 5, wherein said means for scanning transversely comprises a plurality of photodiodes positioned sequentially in a line generally normal to said path with the end diodes in the se- 7. In a device as set forth in claim 6, wherein said carrier member comprises a rotatable drum having an inside and an outside and having portions which are at least partially transparent and portions which are nontransparent, which portions define said characters and also define lines at each side of each character which lines form part of said means for identifying which character is in said stage, and means at one of said sides of the drum for shining light through the at least partially transparent portions to produce said visual display, and

said scanning member is stationary on the other of said sides of the drum in a position at which the light from said at least partially transparent portions falls on said scanning means.

a r I g A J; UNITE STATES PATENT OFFICE Y i 4 gc fr Tj I FIcATE OF coRRtcTIoN Peek-"J w I 7 that error appears in the above-identified patent and that';saidLe'tteirsPatent are hereby corrected as shown below:

After "produces a" delete "scanning character images in matrix'formon a photographic master. lines." and insert rectangular raster consisting of many closely-spaced (or I just overlapping) parallel lines.-

Q le jne uzo, 21, 22 After "scanner C. R. T., change -I' H "SCANNING CHARACTER IMAGES IN MATRIX FORM' ON A PHOTOGRAPHIC MASTER" t0 lower case.

Col', line 65" v 7 Before "gate" change "OR" to --OR- 4', li nefl66 I Change "pDC" to -PDC-- a change to I l d this 22nd day Of October 1974.

f1 v fittest! v I I v p l A Moor M. :GIBSON JR. c, MARSHALL DANN fT-gjv A'ttesting Officer Commissioner of Patents USCOMM-DC 60876-P69 UNITED STATES PATENT OFFICE I CERTIFICATE 0F QRECTION Patent' No. 3,814,848 Dated June 4, 1974 'w h Derek John Kyte It is cert ified that error appears in the above-identified patent and that sa-id Letters Patent are hereby corrected as shown below:

"Col. l5 line l2 After "produces a" delete "scanning '1 character images in matrix'formon a photographic master. lines." and insert rectangular raster consisting of many closely-spaced (or just overlapping) parallel lines.--

Col. 1, lines 20, 21, 22 After "scanner C.R.T." change I "SCANNING CHARACTER IMAGES IN MATRI) FORM ON A PHOTOGRAPHIC MASTER" t0 lower case,

Col. 4, line 65 Before "gate" change "OR" to OR- Col 4, line 66 Change "pDC" to -PDC- ,Col. 5, line 24 Change "F5" to FD- Signed and sealed this 22nd day of October 1974.

A '(SE-A'L) Attest: McCOY M. GIBSON JR. 0. MARSHALL DANN A'ttesting Officer Commissioner of Patents FORM PC4050 USCOMM-DC eos7e-pce I A t 0.5 GOVERNMENT PRINTING OFFICE Z I969 "-35G-33" 

1. In a device for producing a plurality of electrical signals for typesetting purposes which signals define the shape of a number of visual characters such as letters of the alphabet or the like, the improvement comprising: a character carrier member, a scanning member, means connected to one of said members to move it repeatedly along a given path with respect to the other member so that there is cyclical relative motion between the members along said path with the motion being at a given rate, said character carrier member having means to visually display each of said characters against a photo-differential background in a sequential series parallel to said path so that with said relative motion there is first an approach to a character, then a stage of movement adjacent that character and then a separation from the next character in turn and the scanning member, with said stage of movement adjacent the character taking place in a given period of time, said carrier member having indexing means indicative of which character is in said stage, said scanning member including means for scanning transversely of said path at a rate such that a plurality of sweeps across each character takes place during said stage whereby during each sweep an electrical signal is produced which signal represents a portion of the character and at the time of the subsequent sweep there has been relative motion between the character and the scanning member so that said subsequent sweep traverses, and produces electrical signals indicative of, an adjacent portion of the character, said scanning member including means positioned to sense and respond to said indexing for identifying which character is in said stage.
 2. In a device as set forth in claim 1, wherein said carrier member comprises a rotatable drum having an inside and an outside and having portions which are at least partially transparent and portiOns which are non-transparent, which portions define said characters and also define lines at each side of each character which lines form part of said means for identifying which character is in said stage, and means at one of said sides of the drum for shining light through the at least partially transparent portions to produce said visual display, and said scanning member is stationary on the other of said sides of the drum in a position at which the light from said at least partially transparent portions falls on said scanning means.
 3. In a device as set forth in claim 1, wherein said means for scanning transversely comprises a plurality of photodiodes positioned sequentially in a line generally normal to said path with the end diodes in the sequence being spaced apart sufficient to extend across the corresponding dimension of said visual display.
 4. In a device as set forth in claim 3, wherein said carrier member comprises a rotatable drum having an inside and an outside and having portions which are at least partially transparent and portions which are non-transparent, which portions define said characters and also define lines at each side of each character which lines form part of said means for identifying which character is in said stage, and means at one of said sides of the drum for shining light through the at least partially transparent portions to produce said visual display, and said scanning member is stationary on the other of said sides of the drum in a position at which the light from said at least partially transparent portions falls on said scanning means.
 5. In a device as set forth in claim 1, wherein said indexing means includes a visual mark transverse to said path and positioned between each character and further visual marking means to identify each time that the cycle of relative movement repeats.
 6. In a device as set forth in claim 5, wherein said means for scanning transversely comprises a plurality of photodiodes positioned sequentially in a line generally normal to said path with the end diodes in the sequence being spaced apart sufficient to extend across the corresponding dimension of said visual display.
 7. In a device as set forth in claim 6, wherein said carrier member comprises a rotatable drum having an inside and an outside and having portions which are at least partially transparent and portions which are non-transparent, which portions define said characters and also define lines at each side of each character which lines form part of said means for identifying which character is in said stage, and means at one of said sides of the drum for shining light through the at least partially transparent portions to produce said visual display, and said scanning member is stationary on the other of said sides of the drum in a position at which the light from said at least partially transparent portions falls on said scanning means. 